Heat and Cold Stress Course: Lessons 2026

Lesson 1: Your body, heat, cold and the law

Your body works best with a core temperature of about 37°C. CCOHS says a change of more than 1°C is a sign of illness or of conditions the body cannot cope with. Heat stress is the total heat load on a worker from hard work, the weather or the building, and clothing.

Two weather numbers help you judge risk. Humidex shows how hot it feels when heat and humidity combine. Wind chill shows how cold it feels when wind is added. CCOHS says humidex is meant for the general public, so workplaces must use it with caution. Safety experts measure workplace heat with other tools.

What the law expects

• Ontario: the province's heat stress guidance points to the OHS Act, which says employers must take every reasonable precaution to protect workers. This can include protection from heat stress.
• British Columbia: OHS Regulation Part 7, Division 4 requires a heat stress assessment and exposure control plan (s. 7.29) and a cold stress assessment and plan (s. 7.34) where there is a risk.
• Rules differ in each province and territory, so check your own.

Lesson 2: Heat illnesses and first steps

Heat stroke is a medical emergency. The skin may be hot and dry, but a person who did hard work may still be sweating, so sweat does not rule it out. While you wait for help, move the person to shade, remove extra clothing, wet the skin and put cold, wet cloths or ice on the head, neck, armpits and groin. Do not force them to drink.

Heat exhaustion can turn into heat stroke. Never leave the person alone.

Lesson 3: Preventing heat stress

Drink water often

CCOHS advises about 250 mL (one cup) every 20 minutes, even if you are not thirsty, and no more than 1.5 litres an hour. Employers should provide cool water near the work area. BC's regulation requires an adequate supply of cool drinking water close to the work area (s. 7.31). Avoid alcohol and drinks with lots of caffeine or sugar.

Get used to the heat

Acclimatization means the body adjusts to heat over several days. CCOHS suggests new workers start with no more than 20% of normal exposure on day 1, adding no more than 20% a day. Ontario's guidance suggests building up over one to two weeks, and says workers who were ill or away for 9 days or more need to re-adjust.

Plan the work

• Use engineering controls first, such as shade, air conditioning and good air flow
• Do heavy tasks in the cooler morning or evening
• Take more and shorter breaks in a cool rest area
• Wear light, loose clothing and cover your head outdoors

Humidex guide

Lesson 4: Cold injuries and first steps

Hypothermia starts when the core temperature falls below 35°C. Early signs are shivering, poor judgement, trouble forming words and clumsiness. As it gets worse, shivering may stop and the person may become unresponsive. It is a medical emergency.

• Get medical help and move the person out of the cold.
• Have them lie down and handle them gently. Do not rub the skin.
• Warm the chest, armpits, groin and upper back with blankets or warm packs.
• Do not rewarm too fast with a heat lamp, stove or hot bath.
• Give warm, non-alcoholic drinks only if they are alert and only mildly cold.

Frostnip and frostbite

Frostnip is the mildest freezing injury and a warning that frostbite is starting. Frostbite happens when body tissue goes below 0°C. Skin may look waxy and feel colder and harder than the skin around it, and numbness is often the first sign. If skin is only numb or tingly, warm it right away, for example hands under your armpits. If it is frostbitten, get medical help and keep it from getting colder, but CCOHS says not to try to rewarm it on site. Do not rub it or use snow, and do not thaw it if it could freeze again.

Cold and wet

Trench (immersion) foot comes from feet staying cold and wet for a long time. CCOHS says it can happen at temperatures as high as 15.5°C. Keep feet dry and change wet socks.

Lesson 5: Working safely in the cold

Dress in layers

• An inner layer that wicks sweat away from the skin
• Middle layers that insulate; wool and synthetics stay warm when wet
• A wind- and water-resistant outer layer that is easy to take off
• A hat that covers the ears, and mittens when it is below -17°C
• Avoid cotton next to the skin, because it gets damp quickly

Wet clothing loses its warmth fast. Pace your work so you do not sweat heavily, and change into dry clothes if you get wet.

Breaks, shelter and food

• Take regular warm-up breaks in a heated place.
• In BC, a nearby heated shelter must be available when the equivalent chill temperature is below -7°C (s. 7.36).
• For work at -12°C or colder, CCOHS guidance includes a buddy or supervisor keeping constant watch.
• Eat regular meals and drink warm, non-alcoholic drinks or soup. Alcohol gives a false feeling of warmth.

If a worker shows signs of cold stress, remove them from the cold. BC's regulation says they must be removed from further exposure and treated (s. 7.38).